The present invention relates to a lifting loop of the type comprising a core of parallel threads enclosed in a protecting covering which is retained in position about the core by means of a seam stitched in the longitudinal direction of the loop.
Lifting loops or slings are already known which are provided with a central seam penetrating entirely through the core of the sling. This central seam draws together the centre portion of the sling in such a manner as to render the core compact and ensure that the covering encloses the latter snugly and securely.
One drawback of producing roundslings with a central seam of this type is that the design of sewing machines imposes a reduction of the size (coarseness) of the sling and therefore of its load-bearing capacity and strength to comparatively low values. Another drawback is that the central seam is exposed to wear from the load carried by the sling or from the lifting hook from which the sling is suspended, and therefore the seam often breaks before the breaking point of the sling is reached. Once the seam snaps off at one point, the core threads no longer are kept tightly together at this point that thus forms a weakened zone of the sling, which needs replacement or repair.
To eliminate the drawbacks outlined above, seamless roundslings may be produced. Such slings are manufactured by positioning a covering in the form of a hose around a tightly closed bundle of fibres, whereafter the ends of the covering are placed in overlapping position and are interconnected. However, this method is complicated and it is difficult to fill the covering to a satisfactory degree, with the result that during loading operations the fibres might be shifted and their orientation therefore disadvantageous. As a consequence they may be unevenly loaded, which causes ruptures of individual fibres and therefore a reduction of the load-bearing capacity of the loop.